If they're installed, then you should be able to (assuming if needed the E to G route (that is the one, right?) is also installed). I guess you'd have to manually choose them. For obvious reasons they won't spawn when on foot.
Have got the Edinburgh Glasgow route installed but the 66’s still don’t show up on the Midland Main Line route
Uninstalled &reinstalled both the DRS 66 & the One 66 but still no joy. Would installing the Cargo Line Wagons make any difference
I personally wouldn't imagine that would help, since it's the 66s that aren't showing up, not the wagons.. but you could always try just in case! Good luck!!